Experimental Investigation on Acoustic Effects of Trailing Edge Modifications of Splitter Attenuators for Power Generation Systems

Regular paper

Cecilia Sebastiani

Mueller-BBM GmbH

Monday 1 june, 2015, 18:00 - 18:20

0.6 Madrid (49)

Splitter attenuators are used in a wide range of applications, including high-end silencers for power generation systems. Usually this type of device represents the last stage for noise reduction in the exhaust stacks of power plants, i.e. any sound generated downstream of the silencer is radiated into the open without any relevant attenuation. As national regulations demand increasingly strict noise limits, silencers in exhaust stacks need to be designed to achieve the necessary high acoustic insertion losses. With the upstream noise reduced to ever lower levels, the effect of the self-noise generated by the splitter itself - as a bluff body immersed in the flow - becomes critical for the overall performance of the silencing system. Because the typical operative conditions in exhaust stacks (e.g. high temperatures, difficult access, undefined parameters, etc.) make an in-depth study of the problem in real installations essentially impossible, a study on the acoustic optimization of the splitter trailing edge geometry has been performed under laboratory conditions. This paper summarizes the results obtained in an experimental campaign conducted in the framework of FlowAirS Project – ITN FP7, Marie Curie Actions. Sound measurements on several fully functional splitters scaled 1:3 with Mach and Reynolds number similarity to the typical conditions in an exhaust stack have been performed. Different trailing edge shapes including tapered and serrated extensions have been tested. Only moderate changes in the measured noise have been found, despite a reduction of the total pressure loss that can be achieved by appropriate design of the splitter trailing edges. The results are analyzed applying Nelson and Morfey’s theory for obstacles in ducts, which is found to be only partially applicable to the case under study. Furthermore, the relevance of Ffowcs Williams and Hall’s theory for noise resulting from edge scattering of boundary layer turbulence is assessed.

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